BACKGROUND: Relationships between red blood cell (RBC) transfusion, circulating cell-free heme, and clinical outcomes in critically ill transfusion recipients are incompletely understood. The goal of this study was to determine whether total plasma heme increases after RBC transfusion and predicts mortality in critically ill patients.
STUDY DESIGN AND METHODS:This was a prospective cohort study of 111 consecutive medical intensive care patients requiring RBC transfusion. Cellfree heme was measured in RBC units before transfusion and in the patients' plasma before and after transfusion.RESULTS: Total plasma heme levels increased in response to transfusion, from a median (interquartile range [IQR]) of 35 (26-76) μmol/L to 47 (35-73) μmol/L (p < 0.001). Posttransfusion total plasma heme was higher in nonsurvivors (54 [35-136] μmol/L) versus survivors (44 [31-65] μmol/L, p = 0.03). Posttransfusion total plasma heme predicted hospital mortality (odds ratio [95% confidence interval] per quartile increase in posttransfusion plasma heme, 1.76 [1.17-2.66]; p = 0.007). Posttransfusion total plasma heme was not correlated with RBC unit storage duration and weakly correlated with RBC unit cell-free heme concentration.
CONCLUSIONS:Total plasma heme concentration increases in critically ill patients after RBC transfusion and is independently associated with mortality. This transfusion-associated increase in total plasma heme is not fully explained by RBC unit storage age or cell-free heme content. Additional studies are warranted to define mechanisms of transfusion-related plasma heme accumulation and test prevention strategies.R ed blood cell (RBC) transfusion is associated with increased risk of death in critically ill patients. 1 This risk may be explained by storage-related changes in banked RBCs. Such changes include depletion of adenosine triphosphate, nitric oxide, and 2,3diphosphoglycerate, excess cellular stiffness and fragility, and low-grade hemolysis. [2][3][4][5] The resulting cell-free hemoglobin (Hb; free in solution and contained in RBC microparticles) 3,4,6-8 can undergo oxidation and release cellfree heme. 9,10 These mediators may cause toxicity when transfused because cell-free Hb promotes circulatory dysfunction by scavenging nitric oxide 4,7,11,12 and cell-free ABBREVIATIONS: ICU = intensive care unit; IQR = interquartile range; MICU = medical intensive care unit; NTBI = non-transferrinbound iron; SOFA = sequential (sepsis-related) organ failure assessment. From the PIETROPAOLI ET AL.Fig. 5. Relationship between posttransfusion total plasma heme concentration and the pretransfusion plasma haptoglobin concentration. Box plots show the median (horizontal line) and 25th and 75th percentiles (lower and upper limits of the box).The dots represent outliers beyond the whiskers that designate the 10th and 90th percentiles. Comparison was made with Kruskal-Wallis test.